Chemical polishing of metals



Unite CHEMICAL POLISHING OF METALS No Drawing. Application March 25, 1957 Serial No. 647,980

8 Claims. (Cl. 41-42) This invention relates to the chemical polishing of metals; more particularly it relates to the chemical treatment of metals to impart thereto a smooth, bright polished surface.

Many attempts have been made heretofore to produce polished surfaces on metals, particularly copper and aluminum and their copper-rich or aluminum-rich alloys, by dipping in various combinations of chemicals. Somewhat attractive results have been obtained by such use of phosphoric acid alone or in combination with substances including acetic acid, sulfuric acid, chromic acid, and hydrogen peroxide.

Such previously-known processes were not altogether satisfactory for several reasons, for example, they imparted insuificient brightness, they caused etching and pitting, the solutions were highly unstable and could not be satisfactorily regenerated.

It is an object of this invention to provide an improved process for the chemical polishing of metals.

It is anothe robject of this invention to provide an improved highly stable polishing composition for the chemical polishing of metals, which composition may be readily regenerated.

It is still another object of this invention to provide an improved process for the chemical polishing of copper, copper-rich alloys, aluminum, and alumimun-rich alloys.

Other objects of this invention will appear hereinafter.

The objects of this invention may be achieved, in general, by contacting a metal surface with a solution containing monoperphosphoric acid, ortho-phosphoric acid and water at a temperature between 90 C. and 130 C.

The content of monoperphosphoric acid, H PO in the solution should preferably be between 0.3 and 5.4 percent, the ortho-phosphoric acid between 70 and 80 percent, and the water between about 15 and 25 percent, and to obtain optimum results the solution should contain 0.5% to 3% monoperphosphoric'acid, 73% to 79% ortho-phosphoric acid, and 18% to 23% water. Although generally not present in ortho-phosphoric acid, the presence of metaor pyro-phosphoric acid is not objectionable.

The contact or treatment time ofthe metal surface with the solution is from ten seconds to four minutes and preferably between thirty seconds and one and one-half minutes. The temperature of. treatment should preferably be within the range 90 C. to 110 C.

The metal object after treatment by immersion, spraying brushing, or the like, is removed and rinsed with Water which preferably contains to 1% nitric acid, after which it is dried. The drying may be carried out at room temperature or at an elevated temperature, preterably below about 100 C.

Metals which are most readily polished by the process of this invention include aluminum, aluminum-rich alloys, i. e., alloys containing in excess of 50% aluminum, copper, copper-rich alloys, i. e., alloys containing at least tates atent 50% copper, c. g., brass, German silver, bronze, and the like.

The metals, prior to contact with the polishing solu tions of this invention if soiled may be cleaned and degreased in a manner well known in the art.

The polishing solutions of this inventions are quite stable and may be maintained at the requisite strength or regenerated to top strength by the simple addition of the required amounts of the ingredients to produce the composition ranges above set forth. Aluminum or magnesium, dissolved from alloys, may be contained in the polishing solution up to 3% without noticeable efiect on the stability of the solution. Dissolved copper, however, will reduce the stability of the bath. If the copper content exceeds about 1% of the solution it may be desirable to discard the solution rather than regenerate the same by addition of monoperphosphoric acid.

The following examples are given to illustrate the details of the invention, it being understood that the specific details set forth therein are not necessarily limitative of the invention.

Example} A clean brass strip having the approximate composition of 67% copper and 33% zinc is immersed in a solution composed of and having a temperature of about C. for fifteen seconds. The strip is immediately rinsed with clean, cold tap water and dried at room temperature. The brass strip is visibly brightened to remarkable extent from a rather dull appearance to an appearance resembling a mirror.

The following five examples show the polishing of strips of aluminum alloy 1100 containing the following approximate analysis: 1.0% silicon and iron, 0.2% copper 0.05% managnese, 0.10% zinc, 0.15% other metals, 99.0% min. aluminum. The compositions and temperatures of the polishing solutions, the period of immersion, and the gloss of the polished aluminum are tabulated in these examples. The gloss measurements were made on a Hunter multipurpose reflectometer. The mirror supplied with the instrument was used as a secondary standard with a gloss value of 10.0. This gloss of the mirror was checked against a black gloss standard and the value obtained was within experimental error. In each example the aluminum strips, after treatment in the polishing solution, were rinsed with cold tap water and dried at room temperature.

' Soln. Time of Example Solution Composition (Percent) Temp. Immer- Gloss (O.) sion (seconds) Ortho-phosphoric acid, 80.8.- II Mouoperphosphoric acid, 2.4. Water, 16.8 Ortho-phosphoric acid, 81.2.---

In Mouoperphosphoric acid, 1.9.. 108 30 8. 4 Water, 16.1.... 103 60 9. 7

Dissolved Metal, 0.8 Ortho-phosphoric acid, 72.2.--. IV Monoperphosphoric acid, 2.4.. 96 60 e 8.3 Water, 25.2... 100 60 9. .3

Dissolved Metal, 0.2. Ortho-phosphoric acid, 7 v Monoperphosphoric acid, 1.8.. 103 00 9 3 Water, 19.6.-......... 101 30 7. 5

ODislslolveild Mgtal, 0.2.6.725.-. rt o-p osp oric aci VI Monoperphosphoric acid, 1.7.. 8g Water, 23.2

Example VII O. See. Gloss Ortho-phosphoric acid, 75.8 percent 103 60 9 6 Monoperphosphoric acid, 2.7 percent v 105 60 9 2 Water, 21.4 percent 103 30 7 8 Similar polishing was obtained by treating aluminum alloys Nos. 1175, 3003 and 6 063 insolutions of the kind disclosed in the above examples. These aluminum alloys have the following compositions:

Alloy 1175:

0.15% silicon+iron 0.10% copper 99.75% min. aluminum Alloy 3003:

0.6% silicon 0.7% iron, 02% copper 10-15% manganese 0.1% zinc 0.15% other metal, Remainderaluminum Alloy 6063:

0.2-0.6% silicon 0.35% iron 0.10% copper OAS-0.9% magnesium 0.10% chromium 0.10% zinc 0.10% titanium 0.15% other metal remainder -aluminum The polishing compositions of the present invention are fast acting, non-pitting, stable compositions which are readily maintained or brought up to requisite treatment strength.

The treatment of metal surfaces can be carried out on metal objects havingciuite irregular surfaces to produce a uniform polished appearance.

Throughout the specification and claims, any reference to parts, proportions and percentages refers to parts, proportions and percentages .by weight unless otherwise specified.

Since it is obvious that many changes and modificationstions can be made in the above-described details without departing from the nature and spirit of the invention, it is to be understood that the invention is not to be limited to said details except as set forth in the appended claims.

We claim: a

1. A metal polishing composition containing'0.3% to 5.4% monoperphosphoric acid, to phosphoric acid, and 15% to 25% water.

2. A metal polishing composition containing 0.5% to 3% monoperphosphoric acid, 73% to 79% phosphoric acid, and 20% to 23% water.

3. The process of polishing a metal surface which comprises contacting the same at a temperature of C. to 130 C. with a solutionvcontaining monoperphosphoric acid, a phosphoric acid, and water.

4. The process of polishing a metal surfacewhich comprises contacting the same at a temperature of 90 C. to 130 C. with a solution containing 0.3% to 5.4% monoperphosphoric acid, 70% to 80% phosphoric acid, and 15% to 25% water.

5. The process of polishing a metal surface which comprises contacting the same at a temperature of C. to C. with a solution containing 0.5 to 3%rnonoperphosphoric acid, 73% to 79% phosphoric acid, and 20% to 23% Water.

6. The process of claim 3 in which the metal is from the group consisting of aluminum, aluminum-rich alloys, copper, and copper-rich alloys.

7. The process of claim 4 in which the metal is from the group consisting of aluminum, aluminum-rich alloys, copper, and copper-rich alloys.

8. The process of claim 5 in which the metal is from the group consisting of aluminum, aluminum-rich alloys, copper, and copper-rich alloys.

No references cited.

UNITED STATES PATENT OFFICE v CERTIFICATE OF CORRECTION Patent No. 2,834,659

May 13, 1958 Owen B, Mathr-e et al. I

of the above numbered pa on and that the said Letters Patent should read as corrected below.

Colunm 3, under the heading insert O.,l0%

Alloy 6063:" following manganese "0.10% copper" Signed and sealed this 15th day of July 1958.

(SEAL) Attest:

KARL Ha AXLINE ROBERT C. WATSON Attesting Oflicer Commissioner of Patents 

5. THE PROCESS OF POLISHING A METAL SURFACE WHICH COMPRISES CONTACTING THE SAME AT A TEMPERATURE OF 100* C. TO 110*C. WITH A SOLUTION CONTAINING 0.5 TO 3% MONOPERPHOSPHORIC ACID, 73% TO 79% PHOSPHORIC ACID, AND 20% TO 23% WATER. 